1. Field of the Invention
The present invention relates to an image processing apparatus, an image printing apparatus and a printing data generation method, and specifically to printing data generation used for a printing apparatus that performs printing by forming different sizes of dots.
2. Description of the Related Art
Printing apparatuses are used as apparatuses that perform printing such as printers, copy machines, and facsimile machines, or output apparatuses for composite electronics apparatuses including such as computers and word processors, workstations and the like. These printing apparatuses are configured so as to print images and the like on printing media such as paper or plastic sheets based on image information (including all output information such as character information).
Among these printing apparatuses, inkjet type apparatuses perform printing by ejecting ink from a printing head onto printing media. This type of printing apparatus has various advantages of easily realizing a higher printing resolution, high speed, low noise and low production cost. An inkjet printing apparatus uses a printing head provided with an ejection opening line, arranged with a plurality of ink ejection openings, for each ink color. Thus the use of a printing head arranged with many ejection openings may improve printing throughput.
In recent years, need for color printing has been increased and there are provided many color inkjet printers capable of high image quality printing comparable to silver halide photography.
A known example of a configuration for inkjet printing apparatus, which is capable of such high image quality printing, performs printing by forming dots with a plurality of sizes for one color (Japanese Patent Laid-Open No. 10-016251 (1998)). This configuration can reduce granularity in a highlight portion of an image by using relatively small dots preferentially and increase density in a dark portion even with fewer dots by using relatively large printing dots preferentially.
Furthermore, Japanese Patent Laid-Open No. 2002-301815 makes a proposal to perform quantization for printing data generation of such dots with a plurality of sizes independently for each of the different sizes of dots in order to improve a degree of freedom in dot arrangement design for printing quality and the like.
However, the configuration, in which printing data generation is performed independently for each different size of dot as described in Japanese Patent Laid-Open 2002-301815, increases an amount of data generated or processed according to the number of sorts of dot size used for printing. In an embodiment of Japanese Patent Laid-Open 2002-301815, dots with two sorts of sizes; large and small, are used for each color of cyan (C), magenta (M) and yellow (Y), and, in this case, printing data of large and small dots for each color is generated by quantization to be 4 bit data, respectively. Therefore, a data amount of 4 bits per one pixel is increased each time a sort of dot size is increased by one for each color. The increase of data amount may cause the following problem.
For example, when printing data is transferred from a host apparatus to a printer, increase of an amount of data to be transferred may cause a situation that transferring is not as fast as printing at the printer side. In such a case where transfer speed of printing data is not as high as printing speed of a printing apparatus, the printing apparatus has to wait for the printing data and is required to stop printing randomly every time waiting of printing data occurs during printing the data, resulting in deterioration of throughput or printing quality.
Not limited to the case where a host apparatus generates printing data, there is also a case that increase of an amount of data to be processed is not preferable even in a configuration in which printing data is generated within a printing apparatus. For example, memory capacity is required to be increased according to a number of dot sizes used for printing, resulting in causing a problem such that usage of the memory is limited in the printing apparatus.